In a flat display, for example, a liquid crystal display (LCD), an organic electroluminescent display or an inorganic electroluminescent display, a thin-film transistor (TFT) is generally used as a switch element to control the working of a pixel or as a driving element to drive a pixel. According to the property of the silicon thin film thereof, the thin-film transistor may usually be divided into amorphous silicon (a-Si) and polysilicon (poly-Si). In comparison with the amorphous silicon thin-film transistor, the polysilicon thin-film transistor has higher electron mobility, better liquid crystal features and smaller leakage current. Thus, a display made of polysilicon thin-film transistors will have a higher resolution and a faster response speed. The low-temperature polysilicon technology is gradually replacing the amorphous silicon technology and becoming a main stream of the research and development of thin-film transistors.
However, a process for preparing a polysilicon thin-film transistor array substrate has many disadvantages; for example, the process is complex, and the cost is high, etc. A typical polysilicon thin-film transistor array substrate employs a mask plate for 9 times, which is more complex and time-consuming in comparison with the general amorphous silicon thin-film transistor array substrate that employs a mask plate for 5 or 6 times, thus the capacity of industrialized production is lowered greatly, and the cost is increased.